The present invention relates to methods and compositions for treating subterranean formations, and more specifically, to improved breaker compositions for synthetic polymers, and methods for reducing the viscosity of viscosified treatment fluids.
Synthetic polymers, which include polymers that do not occur naturally but may be formed artificially from petrochemicals, may be used in a variety of subterranean treatment fluids that may be used in a variety of operations and treatments conducted in oil and gas wells. As used herein, the term “treatment fluid” refers to any fluid that may be used in a subterranean application in conjunction with a desired function and/or for a desired purpose. The term “treatment fluid” does not imply any particular action by the fluid or any component thereof. Such operations and treatments include, but are not limited to, stimulation, completion, fluid loss control operations, and other similar applications.
In fracturing operations, synthetic polymers are often added to treatment fluids to form viscosified treatment fluids. After the operation, to recover (and possibly recycle) the fluid, oftentimes the viscosifying synthetic polymer is broken (e.g., by breaking its backbone and/or polymer chains) so that the viscosity of the fluid is reduced, thereby allowing the fluid to flow back to the surface and be recovered. This process may be referred to in the art as “breaking the fluid.” Compositions that are used in this process to interact with the polymer so as to reduce the viscosity of the fluid may be referred to in the art as “breakers.”
Generally, the synthetic polymers used in subterranean application may be of high molecular weight and contain hydrocarbon backbones, which may be hard to break in a controlled manner. An example is a copolymer of acrylamide and acrylic acid that has a high molecular weight and can be used as a friction reducer. It contains a hydrocarbon backbone that may be hard to break. Often these polymers adsorb onto the formation or become incorporated within a filter cake. Because such polymers may be difficult to break, their incomplete removal from the filter cake ultimately may affect the permeability of the formation.
Furthermore, breaking viscosified fluids at lower temperatures, e.g., 60° F. to 150° F., may be challenging. Typically greater amounts of oxidizers may be needed to break these polymers at low temperatures. Attempts to obtain delayed controlled break times by reducing the concentration of breakers generally may result in incomplete breaks of the polymer and may be damaging to the permeability of the producing zone. The traditional hypochlorite breakers used to break these polymers at low temperature also may suffer from other disadvantages such as corrosion of pipes, generation of residue, generation of chlorine gas (when mixed with certain brines), uncontrolled break, etc. For high temperature (>150° F.) wells, sodium perborate may break the polymers, but at low temperature the breakage may be slow and may not reach completion before all the hydrogen peroxide generated is consumed.
Similarly, synthetic polymers may be used in other applications described previously where they need to be broken before they can be removed from the formation. Furthermore, in tools applications, there may be a need for some elastomeric parts, e.g., rubber parts, to degrade after a delay period at low temperatures. Currently there is no chemical method available with service companies to break the rubber components.